Unusual Association of Skipjack Tunas Katsuwonus pelamis and a Longline Vessel

Ocean Science Journal - Skipjack tuna were observed for the first time swimming in front of the bow of a fishing vessel during a tagging campaign in the North Atlantic. Video recordings show how...     

Comparison of Grid Averaged Altimeter and Buoy Significant Wave Heights in the Northern Indian Ocean

A quantitative comparison of the collocated inter-annual significant wave height (SWH) data collected between 2006 and 2009 from buoys and altimeters at nine buoy locations (total n = 2241) in the Northern Indian Ocean is attempted for assessing the validity of daily averaged gridded altimeter significant wave height (ASWH) provided by AVISO for operational use. ASWH is underestimated by 0.20 m, the root-mean-square error (RMSE) is less than 0.30 m, the Scatter Index is less than 20%, and the correlation coefficient is greater than 0.90. Further, at three locations, the examination of the above statistics showed that the bias and RMSE is high during the southwest monsoon season compared with the Northeast monsoon. Scatter Index showed only slight variation (14–18%) for different ranges of SWH. The response of the daily average gridded ASWH data during extreme conditions (cyclones) in the vicinity of the buoy locations is poor at all compared buoy locations. The gridded ASWH from different satellite missions provided by AVISO can be used for basin scale validation experiments of the wave model and for climatological studies in the Indian Ocean, except during cyclone conditions.     

Microscale Response of Sediment Variables to Benthic Disturbance in the Central Indian Ocean Basin

Abstract

The response of sediment bacteria and biochemical variables to benthic disturbance was investigated in the Central Indian Ocean Basin from cores at nine stations. Generally, bacterial density and biochemical variables declined vertically with depth in the upper layers of the cores. Mechanical disturbance caused by a hydraulic disturber brought about a substantial decrease in total bacterial numbers. However, the numbers of retrievable bacteria increased by two orders of magnitude. The biochemical parameters decreased in quantity with a shift in the linear relationship. The data suggest that abiotic artifacts will directly affect the biomass and biochemistry of the sediment.     

A Methodology for Simulating Radionuclide Diffusion in Unsaturated Soils

In this paper, a methodology that can be employed to simulate radionuclide migration through unsaturated soils, under laboratory conditions, has been developed and reported. This was achieved with the help of a specially designed half-cell setup to study diffusion characteristics of inactive forms of Cs⁺, Sr⁺² and Co⁺² in two different types of soils, corresponding to their different compaction states. It has been noted that the apparent diffusion coefficient strongly depends on the volumetric water content of the soil. However, increase of the apparent diffusion coefficient for higher volumetric water contents is found to be much less as compared to the lower volumetric water contents.     

Geochemical characterization of source rock from the north bank area,upper Assam basin

The study area is confined to a part of upper Assam basin, north of river Brahmaputra (north bank). Seven exploratory wells have been drilled in this part of the basin in order to probe the hydrocarbon prospects of the area. The exploratory efforts did not indicate significant hydrocarbon prospects in the north bank. Since the presence of source rock is an important component of the petroleum system, a detailed systematic study of source rock potential was carried out by analysing known source rock intervals in these seven wells. In the present study, Rock-Eval pyrolysis combined with specific geochemical analyses like GC and TLCFID has been used to characterise the source rocks, their distribution and thermal maturity of the organic matter. The source rocks in the area show mainly Type III, land-plant derived organic matter along with some Type II organic matter. They are predominantly gas prone in nature, although mixed and oil-prone source rocks are occasionally present. Although source rock intervals have been identified in the Langpar, Sylhet limestone and Kopili formations, the Barail Group and the Tipam sandstone Formation, the bulk of the source rock occurs within the Kopili Formation. Geochemical analyses of the cores indicate oil signatures at certain depths, although no commercial oil was discovered. The hydrocarbon generation potential of these source rocks are constrained by low maturity at the presently drilled depths.     

Basement tectonics and flexural subsidence along western continental margin of India

The Paleocene-recent post-rift subsidence history recorded in the Mumbai Offshore Basin off western continental margin of India is examined. Results obtained through 2-D flexural backstripping modelling of new seismic data reveal considerable thermo-tectonic subsidence over last ca. 56 Myr. Reverse postrift subsidence modelling with variable β stretching factor predicts residual topography of ca. 2000 m to the west of Shelf Margin Basin and fails to restore late Paleocene horizon and the underlying igneous basement to the sea level. This potentially implies that:(1) either the igneous basement formed during the late Cretaceous was emplaced under open marine environs; or(2) a laterally varying cumulative subsidence occurred within Mumbai Offshore Basin(MOB) during ca. 68 to ca. 56 Ma. Pre-depositional topographic variations at ca. 56 Ma across the basin could be attributed to the extensional processes such as varied lower crustal underplating along Western Continental Margin of India(WCMI). Investigations about basement tectonics after unroofing of sediments since late Paleocene from this region support a transitional and heavily stretched nature of crust with high to very high β factors. Computations of past sediment accumulation rates show that the basin sedimentation peaked during late Miocene concurrently with uplift of Himalayan-Tibetan Plateau and intensification of Indian monsoon system. Results from basin subsidence modelling presented here may have significant implications for further studies attempting to explore tectono-climatic interactions in Asia.     

Granite-molybdenite association in Kerala in relation to taphrogenic metallogeny

Two molybdenite-bearing granites from the Kerala region, namely, the Chengannoor and the Ambalavayal granites are discussed here in terms of their salient geochemical characters. The geochemistry of the host rocks indicates a peraluminous, calc-alkaline to alkali-calcic nature and the element levels show good fit with the proposed ‘finger-prints’ for granite-molybdenite systems. Fluid inclusion studies suggest that Mo was probably partitioned in vapour phase, which subsequently combined with available sulphur. Regional distribution of molybdenite strongly favours the view of a molybdenum province in the southern part of the Indian shield. Associations of rare metal mineralization with the riftcontrolled acid magmatic phase in the Kerala region are suggestive of a late Precambrian —Early Palaeozoic taphrogenic metallogeny.     

Impact of Land Surface Heterogeneity on Mesoscale Atmospheric Dispersion

Prior numerical modelling studies show that atmospheric dispersion is sensitive to surface heterogeneities, but past studies do not consider the impact of a realistic distribution of surface heterogeneities on mesoscale atmospheric dispersion. While these focussed on dispersion in the convective boundary layer, the present work also considers dispersion in the nocturnal boundary layer and above. Using a Lagrangian particle dispersion model (LPDM) coupled to the Eulerian Regional Atmospheric Modeling System (RAMS), the impact of topographic, vegetation, and soil moisture heterogeneities on daytime and nighttime atmospheric dispersion is examined. In addition, the sensitivity to the use of Moderate Resolution Imaging Spectroradiometer (MODIS)-derived spatial distributions of vegetation characteristics on atmospheric dispersion is also studied. The impact of vegetation and terrain heterogeneities on atmospheric dispersion is strongly modulated by soil moisture, with the nature of dispersion switching from non-Gaussian to near-Gaussian behaviour for wetter soils (fraction of saturation soil moisture content exceeding 40%). For drier soil moisture conditions, vegetation heterogeneity produces differential heating and the formation of mesoscale circulation patterns that are primarily responsible for non-Gaussian dispersion patterns. Nighttime dispersion is very sensitive to topographic, vegetation, soil moisture, and soil type heterogeneity and is distinctly non-Gaussian for heterogeneous land-surface conditions. Sensitivity studies show that soil type and vegetation heterogeneities have the most dramatic impact on atmospheric dispersion. To provide more skilful dispersion calculations, we recommend the utilisation of satellite-derived vegetation characteristics coupled with data assimilation techniques that constrain soil-vegetation-atmosphere transfer (SVAT) models to generate realistic spatial distributions of surface energy fluxes.     

Gold Mineralization in Kottathara Prospect, Attappadi Valley, Kerala, India: a Preliminary Appraisal

The Kottathara gold prospect of Attappadi Valley in Kerala is located within the Southern Indian Granulite Terrain comprising charnockite and gneisses with enclaves of high-grade supracrustals. The gold mineralization associated with the basic members of the Attappadi supracrustals and the quartz veins traversing them are confined within the Bhavani Shear Zone. Primarily the gold-quartz lode is emplaced in rheologically preferred zones along the contact of the basic members with the enclosing gneisses subsequent to a period of retrogression and shearing. Ore-mineralogical studies reveal that gold got remobilized and this remobilization is identified with the regional Bhavani Shear. SEM studies indicate that gold occurs in free state and also within sulphides especially pyrite. Variation in grain morphology is clearly discernible in gold occurring within oxidised and in non-oxidised zones.Sequencing of deformational events with associated emplacements of known ages suggests the age of gold mineralization of Attappadi area as between 2 Ga. and 2.5 Ga. The secondary mobilization has to be <2.0 Ga or younger possibly of younger Pan-African age related with the Moyar-Bhavani Shear System. The inherent gold content of the komatiitic metapyroxenites together with the auriferous quartz lodes assigns a lithological control on gold mineralisation. Subsequent folding and remobilization due to the regional shear constrained the geometry of the lode zones implying structural control.     

Induced magnetic field of the equatorial electrojet at the surface of the Earth

Summary. The northward component of the induced magnetic field due to the equatorial electrojet at the Earth's surface is calculated using a more realistic local time variaton of the external field due to the electrojet than is provided for by models of the electrojet currently used in induction calculations. It is seen that appreciable induction effects can be expected about an hour before local noon for the kind of local time variation considered. Our results are in qualitative agreement with direct observations of Earth currents in the equatorial region in Nigeria. At local times when observable induction effects are present, the magnetic field due to the electrojet is necessarily three-dimensional; hence in order to obtain the internal part directly from the observed total field due to the electrojet at the Earth's surface, a three-dimensional formulation is required.